Sunlight (solar energy) consists of radio wave, microwave, infrared ray, visible light, ultraviolet (UV) ray, X-ray, γ-ray, and other in the order of decreasing wavelength. In addition, as the negative effect of sunlight on the skin is known, many products for protecting the skin from sunlight have been developed.
However, although sunlight includes electromagnetic waves of various wavelengths as described above, the sunlight protection effect is mostly determined at present only on the basis of the effectiveness of blocking UV. Accordingly, the effect of sunlight protection products is evaluated in terms of the indices for evaluating UV protection, which are sun protection factor (SPF) representing the erythema caused by the light of UVB range (290-320 nm) and protection of UVA (PA) representing the persistent pigment darkening by the light of UVA range (320-400 nm) through a rater's visual observation. In other words, although UV takes a very small portion in sunlight and electromagnetic waves of other wavelength ranges take a larger portion in sunlight, it is unable to verify the effect of sunlight protection of other wavelengths, except the UV protection effect evaluated in terms of the SPF and PA.
Most of commercially available sunlight protection products have been developed by focusing on the UV protection index, such as SPF and PA. Thus, little research and development works have been performed with regard to sunlight protection of visual light.
In addition, although the sunlight protection products have insufficient function of protecting visual light, including the blue/violet light of a wavelength from 400 to 500 nm which causes skin damage the most in the visual light range, it is unable to verify the effect of blue/violet light protection due to the absence of any protection index enabling the evaluation of the blue/violet light protection effect.